Conventionally, an electroacoustic transducer called a “Gamuzon speaker” is such that an acoustic diaphragm having conductor patterns corresponding to a voice coil formed is installed at a pair of intermediate portions of a magnetic field generator, and the acoustic diaphragm is vibrated perpendicular to the vibration plane by supplying a drive current to the conductors.
Since the Gamuzon type electroacoustic transducer has a structure in which conductors are disposed on almost the entire surface of the acoustic diaphragm, the entire surface is driven at the same phase, wherein the electroacoustic transducer has a feature by which a satisfactory transient characteristic can be obtained in a wide range.
The following are proposed as items which belong to such an electroacoustic transducer.    (1) In Japanese Patent Publication No. Sho-35-10420 (hereinafter called Publication (a)), an electroacoustic transducer was proposed, in which adjacent band-shaped magnets (or a band-shaped area in a magnet plate) are disposed with the N and S poles thereof made different from each other, the entirety of a magnet plate including a number of band-shaped magnets is formed to be like a flat plate, and is disposed with the directions of the N and S poles perpendicular to the flat plane, and an acoustic diaphragm, which has conductors formed opposite to the plane of the magnet plate, is disposed.    (2) In Japanese Unexamined Patent Publication No. Sho-51-26523 (hereinafter called Publication (b)), an electroacoustic transducer was proposed, in which an acoustic diaphragm having a conductor deposited between two ring-shaped magnets which are magnetized in the radius direction to the same degree and have uniform thickness, so that the N and S poles are formed on the inner and outer circumferential sides, is disposed, and acoustic waves are radiated from openings formed at the middle of the magnets to the outside thereof.    (3) In Japanese Unexamined Patent Publication No. Sho-59-75799 (hereinafter called Publication (c)), an electroacoustic transducer was disclosed, in which an acoustic diaphragm (plane coil diaphragm) having a pair of flat plate-shaped porous magnet plates opposing each other with fixed spacing in a state repulsing each other, in which the center portion and outer circumferential portion are magnetized with different poles, and having a conductor wound like an eddy therebetween is disposed parallel to the above-described magnet plates.    (4) In Japanese Unexamined Patent Publication No. Sho-52-38915 (hereinafter called Publication (d)), an electroacoustic transducer was described, in which magnet plates (magnetic plates) are constructed with fixed spacing so that a plurality of band-shaped permanent magnets magnetized in the direction parallel to the acoustic diaphragm are disposed with the same poles opposing each other, the above-described magnet plates are disposed on both sides of the acoustic diaphragm having conductors formed thereon, and a number of openings are formed between the band-shaped permanent magnets at the magnet plates on at least one side.    (5) In Japanese Unexamined Patent Publication No. Sho-57-23394 (hereinafter called Publication (e)), an electroacoustic transducer was proposed, in which an acoustic diaphragm is installed, which has a plurality of spiral conductors formed between a pair of flat and porous permanent magnet plates concentrically including a plurality of annular N and S poles, which are divided by an annular transient plane area, in a state where adjacent magnetic poles are turned into different poles, and acoustic waves are radiated from the pores of the magnet plates to the outside thereof.
However, in the above-described prior art electroacoustic transducers, there are the following problems and shortcomings.    (1) In the electroacoustic transducer described in Publication (a), since the N and S poles are disposed with the directions thereof made different from each other by turns, the direction of a magnetic flux greatly changes, wherein the density of the magnetic flux to drive the acoustic diaphragm in the direction perpendicular to the plane, that is, the density (hereinafter called “effective operating magnetic flux density”) of a magnetic flux (hereinafter called an “effective operating magnetic flux”), in which the direction of an electromagnetic force operating in the conductors of the acoustic diaphragm is the vibration direction, greatly changes with respect to the vibration direction, wherein there is a problem in that this becomes a cause of non-linear distortion that deteriorates the acoustic quality.    (2) Where the directions of the N and S poles of the band-like magnets are made different from each other by turns as in Publication (a), the effective operating magnetic flux that becomes parallel to the vibration plane of the acoustic diaphragm increases its density in an area of the acoustic diaphragm opposite to the intermediate portion in adjacent band-shaped magnets, and decreases its density at the portion of the diaphragm opposite to the band-shaped magnets. Therefore, it is difficult to smoothly and continuously form areas having a prescribed effective operating magnetic flux density, and a uniform drive force cannot be obtained on the entire surface of the acoustic diaphragm, wherein a completely entire-surface-drive type speaker having satisfactory vibration characteristics cannot be obtained.    (3) Further, since it is necessary to wind conductors alternately in inverse directions in response to the effective operating magnetic fluxes which alternately become inverse, and to adequately dispose the conductors in an area of narrow width, which has a prescribed magnetic flux density, high working accuracy is required, wherein there is a problem in that productivity thereof is lowered.    (4) In the electroacoustic transducer, described in Publication (b), having an acoustic diaphragm disposed between ring-shaped magnets of uniform thickness, which are magnetized in the radius direction to the same degree, the ring-shaped magnets are not magnetized by partial areas, but are magnetized integrally on the entire inner circumferential side and the entire outer circumferential side so as to form N and S poles. In the case of the ring-shaped magnets, since the total magnetic fluxes at the N pole side and those at the S pole side are always equal to each other although the effective area of the magnetic pole at the outer circumferential side becomes wider than the effective area of the magnetic pole at the inner circumferential side due to a difference in the radius, the magnetic flux density at the outer circumferential side is further lowered than that at the inner circumferential side, and the effective operating magnetic flux density is also lowered. Therefore, the wider the width between the outer diameter of the ring-shaped magnets and the inner diameter thereof, that is, in the radius direction, the larger becomes a difference between the effective area of the outer circumferential side magnetic pole and that of the inner circumferential side magnetic pole, wherein the effective operating magnetic flux density is lowered. Therefore, it was necessary to make the width in the radius direction narrow for use. Accordingly, the design conditions are narrowed, wherein there is a problem in that it is difficult to obtain an electroacoustic transducer which is excellent in the acoustic characteristics adapted to various types of conditions.    (5) In addition, a method for magnetizing the entirety with magnetic poles, which constitute a pair, disposed at the inner circumferential edge side and outer circumferential edge side has been known as the method for magnetizing such a ring-shaped magnet. However, as the width in the radius direction of the ring shape is widened, a difference arises in the magnetization intensity due to a difference in the area of the magnetic poles at the inner circumferential side and outer circumferential side, whereby the inner circumferential portion is first magnetically saturated, and intensive and uniform magnetization was difficult.    (6) In order to reduce such problems of saturation in magnetization and lowering in the above-described magnetic flux density in the vicinity of the outer circumference of the ring-shaped magnets, it was necessary to use a magnet in which the width in the radius direction of the ring shape is narrowed. Therefore, since it is not possible to increase the area between the outer diameter of the ring shape and the inner diameter thereof, that is, of a part contributing to vibrations of the acoustic diaphragm, it is difficult to widely form a highly effective operating magnetic flux density, wherein there is a problem in that the utilization efficiency of the magnetic flux is further deteriorated.    (7) In the electroacoustic transducer using porous magnet plates, which is described in Publication (c), acoustic waves can be discharged outward through acoustic pores formed on the magnet plate. However, the direction of magnetizing the porous magnet plates disposed opposite to each other is made to have an angle by which the entirety of the magnet plates are integrated and concentrated to form N and S poles, wherein since the angle is not adjusted to the optimal angle to increase the effective operating magnetic flux density of the acoustic diaphragm with respect to a conductor, there is a problem in that the utilization efficiency of the magnetic flux is deteriorated. That is, the ratio between value (U) obtained by adding up the effective operating magnetic flux in the conductor of the acoustic diaphragm by the area of the conductor and the total cubic volume (V) of the magnet plates, that is, the effective operating magnetic flux per unit cubic volume of the magnet plates, which is shown by U/V (hereinafter called “effective operating magnetic flux ratio”) is lowered. Further, in the direction of magnetizing such magnet plates, since it is difficult to partially correct the effective operating magnetic flux density of the acoustic diaphragm with respect to the conductor, there is a problem in that a change in the effective operating magnetic flux density of the acoustic diaphragm with respect to the radius direction increases.    (8) In the electroacoustic transducer having a number of openings between the band-shaped permanent magnets, which is described in Publication (d), a number of openings formed in the magnet plates are turned up and disposed in the longitudinal and lateral directions so that the entire arrangement profile thereof becomes rectangular. Therefore, since the arrangement profile of a diaphragm formed like a disk is not coincident with the arrangement profile of the openings that become rectangular, vibrations at the circumferential disk-shaped edges become irregular due to influences in the load distribution of the diaphragm, and there is a problem in that the quality of sound to be reproduced is deteriorated.    (9) Also, since areas having a prescribed effective operating magnetic flux density cannot be continuously formed in the installation position of the acoustic diaphragm, it is not possible to dispose conductors on the entire surface of the acoustic diaphragm, wherein there is a problem in that the entire-surface-drive type speaker cannot be obtained, which has satisfactory vibration characteristics.    (10) In the electroacoustic transducer, described in Publication (e), in which an acoustic diaphragm is installed between a pair of flat porous permanent magnet plates concentrically having a plurality of annular N and S poles divided by annular transient plane areas so that adjacent magnetic poles thereof have a pole different from each other, the annular N and S poles in respective ring-shaped magnets that constitute magnet plates are divided by the annular transient plane areas. That is, the N and S poles are not formed in the partial area units in the respective ring-shaped magnets, but are integrally formed at the entire inner circumferential side and the entire outer circumferential side. In the case of the ring-shaped magnet, although the effective area of the outer circumferential side magnetic pole is made wider than the effective area of the inner circumferential side magnetic pole due to a difference in the radii, the total magnetic fluxes at the N pole side are always equal to the total magnetic fluxes at the S pole side in the magnets. Therefore, even if the magnetic flux density at the outer circumferential side is further lowered than that at the inner circumferential side, the effective operating magnetic flux density is also lowered as shown in FIG. 5B described later. Since the further the ring-shaped magnet in the radius direction is widened, the larger becomes the difference between the effective area of the outer circumferential side magnetic pole and that of the inner circumferential side magnetic pole, it is necessary to narrow the width thereof in the radius direction for use, wherein there is a problem in that the design conditions are limited in terms of obtaining an electroacoustic transducer whose converting efficiency of energy is excellent with a low distortion factor.    (11) Also, a method for magnetizing the entirety of the magnet by disposing a pair of magnetic poles at the inner circumferential edge side and outer circumferential edge side has been publicly known as a method for magnetizing the respective ring-shaped magnets. However, if the width of the ring shape in the radius direction becomes wide, a difference is generated in the magnetizing intensity due to a difference in the area of the magnetic poles between the inner circumferential side and the outer circumferential side, wherein the inner circumferential portion is first magnetically saturated, and intensive and uniform magnetization was difficult. Accordingly, there is a problem in that the width of the ring-shaped magnets in the radius direction is limited.    (12) In order to reduce such problems of saturation in magnetization and lowering in the above-described magnetic flux density in the vicinity of the outer circumference of the ring-shaped magnets, it was necessary to use magnets in which the width of the ring shape in the radius direction is narrowed. Therefore, a combination of a plurality of ring-shaped magnets whose magnetizing directions differ from each other is made into a magnet plate, wherein it was necessary to construct an acoustic diaphragm by combining a plurality of spiral-shaped conductors. Therefore, since such respective combined spiral-shaped conductors independently vibrate (divided vibrations), wherein uniform vibrations of the acoustic diaphragm are obstructed, it was difficult to obtain acoustic characteristics having little distortion.
The present invention was developed to solve the above-described problems, and it is therefore an object of the invention to provide an electroacoustic transducer such as a speaker, headphone, earphone, microphone, acoustic wave sensor, etc., which are able to widely set a distribution of an effective operating magnetic flux density required for a conductor of an acoustic diaphragm and the vibration direction thereof, suppress distortions by uniformly vibrating the acoustic diaphragm, and efficiently convert electric signals into sound, or sound into electric signals, and does not require any high machining accuracy in production.